Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2021	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Statutory federal income tax rate			21.00%	35.00%	35.00%
Income tax expense (benefits) Federal Tax Reform			$ (5.6)	$ (18.1)
Overall income tax rate			8.40%	12.50%	13.40%
Decrease in regulatory assets			$ (16.2)	$ (130.8)	$ (3.6)
Decrease in regulatory liabilities			$ 1.3	$ (83.8)	$ (63.0)
IPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate			21.00%	35.00%	35.00%
Income tax expense (benefits) Federal Tax Reform			$ (1.1)	$ 3.8
Overall income tax rate			(1.20%)	(5.00%)	(2.70%)
Decrease in regulatory assets			$ (20.2)	$ (126.2)	$ (54.7)
Decrease in regulatory liabilities			$ 0.6	$ (71.2)	$ (67.3)
WPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate			21.00%	35.00%	35.00%
Income tax expense (benefits) Federal Tax Reform			$ (5.5)	$ (14.5)
Overall income tax rate			14.80%	24.90%	32.60%
Decrease in regulatory assets			$ 4.0	$ (4.7)	$ 51.1
Iowa Tax Reform [Member] | Alliant Energy and IPL [Member]
Income Tax [Line Items]
Decrease in regulatory assets	$ 33.7
Decrease in regulatory liabilities	$ 7.3
State [Member] | IPL [Member]
Income Tax [Line Items]
Overall income tax rate			12.00%
State [Member] | IPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Overall income tax rate		9.80%